Ceramic insulators have been produced by pressing ceramic batch to form a piece which can be contoured to a desired external shape. A bore extending longitudinally of the piece can be formed by pressing the ceramic batch around an arbor. However, when a need arose for a ceramic piece having a plurality of bores or internal slots extending longitudinally thereof for forming an insulator to be used as a part of an oxygen sensor, no method other than extrusion and subsequent drilling, complex injection molding, or multi-stage precision drilling was available.